Heat/moisture treatment and annealing of starches are taught in the literature.
For example, see the article "Differential Scanning Calorimetry of Heat-Moisture Treated Wheat and Potato Starches" by J. W. Donovan et al. in Cereal Chemistry, Vol. 60, No. 5, pp. 381-387 (1983). See also the article "A DSC Study Of The Effect Annealing On Gelatinization Behavior of Corn Starch" by B. R. Krueger et al. in Journal of Food Science, Vol. 52, No. 3, pp. 715-718 (1987). In both cases, it is observed that the gelatinization temperature of the starches are increased as a result of the heat/moisture treatment or annealing.
The article "Hydrothermal Modification of Starches: The Difference between Annealing and Heat/Moisture-Treatment", by Rolf Stute, Starch/Starke 44, No. 6, pp. 205-214 (1992) defines "annealing" as slurrying the starch with excess water at temperatures below the starch'vs gelatinization temperature and "heat/moisture-treatment" as a semi-dry treatment (i.e., no added moisture with the only moisture being that normally present in the starch granule which is typically 10% or more) at temperatures below the starch's gelatinization temperature. Almost identical modifications in the properties of potato starch were obtained with both treatments even through the alteration of the granular structure was different. The Brabender curves of the heat/moisture-treated and annealed potato starches showed the same typical changes, including a higher gelatinization temperature and a lower peak viscosity or no peak. The DSC curves also showed a shift to higher gelatinization temperatures for both treatments. A combined treatment of annealing a heat/moisture-treated potato starch led to a further increase in gelatinization temperature without detectable changes in gelatinization enthalapy and with the viscosity changes caused by the heat treatment remaining. The heat/moisture-treatment of an annealed potato starch does not lower the gelatinization temperature when compared to the base and increases the gelatinization temperature at higher heat/moisture treatment levels.
The article "Heat-Moisture Treatment of Starches", by Louis Sair, Ind. Eng. Chem., 36, 205 (1944) pages 283-285 discloses starch modification by heating in a pressure cooker at 100% relative humidity. The starch was exposed to steam at 90 to 100.degree. C. for 2 to 18 hours or heated at 27% moisture at 92 to 100.degree. C. for up to 16 hours. The heat/moisture treatment caused rearrangement of and a higher degree of association of the starch chains. There was a change in the X-ray pattern of potato starch from a B form to an A form of the starch molecule.
U.S. Pat. No. 3,977,897 (issued Aug. 31, 1976 to Wurzburg et al.) discloses a method for preparing non-chemically inhibited amylose-containing starches. Both cereal and root starches can be inhibited, but the inhibition effects are more observable with root starches. Amylose-free starches, such as waxy corn starch, showed no or very slight inhibition. The Brabender viscosity of cooked pastes derived from the treated starch was used to determine the inhibition level. Inhibition was indicated by a delayed peak time in the case of the treated corn starch, by the lack of a peak and a higher final viscosity in the case of the treated achira starch, and by the loss of cohesiveness in the case of the treated tapioca starch. The granular starch is suspended in water in the presence of salts which raise the starch's gelatinization temperature so that the suspension may be heated to high temperatures without causing the starch granules to swell and rupture yielding a gelatinized product. The preferred salts are sodium ammonium, maynesiu or potassium sulfate, sodium, potassium or ammonium chloride, and sodium, potassium or ammonium phosphate. About 10-60 parts of salt are used per 100 parts by weight of starch. Preferably about 110 to 220 parts of water are used per 100 parts by weight of starch. The suspension is heated at 50 to 100.degree. C., preferably 60 to 90.degree. C., for about 0.5 to 30 hours. The pH of the suspension was maintained at about 3.0 to 9.0, preferably 4-7. Highly alkaline systems, i.e., pH levels above 9 retard inhibition.
U.S. Pat. No. 4,013,799 (issued Mar. 22, 1977, to Smalligan et al.) discloses heating a tapioca starch above its gelatinization temperature with insufficient moisture (15 to 35% by total weight) to produce gelatinization. The starch is heated to 70 to 130.degree. C. for 1 to 72 hours. The starch is used as a thickener in wet, pre-cooked baby foods having a pH below about 4.5.
U.S. Pat. No. 4,.303,451 (issued Dec. 1, 1981 to Seidel et al.) discloses a method for preparing a pregelatinized waxy maize starch having improved flavor characteristics reminiscent of a tapioca starch. The starch is heat treated at 120 to 200.degree. C. for 15 to 20 minutes. The pregelatinized starch has gel strength and viscosity characteristics suitable for use in pudding mixes.
U.S. Pat. No. 4,302,452 (issued Dec. 1, 1981 to Ohira et al.) discloses smoking a waxy maize starch to improve gel strength and impart a smoky taste. In order to counteract the smoke's acidity and to obtain a final product with a pH of 4 to 7, the pH of the starch is raised to pH 9 to 11 before smoking. The preferred water content of the starch during smoking is 10-20%
GB-A-595,552 discloses treatment of starch, more particularly a corn starch, which involves drying the starch to a relatively low moisture content of 1-2%, not exceeding 3% and subsequently dry heating the substantially moisture-free starch at 115-126.degree. C. for 1 to 3 hours. The treatment is intended to render the starch free from thermophilic bacteria and the starch should not be heated longer than necessary to effect the desired sterilization.
Japanese Patent Publication No. 61-254602, (published Dec. 11, 1987) discloses a wet and dry method for heating waxy corn starch and derivatives thereof to impart emulsification properties. The wet or dry starch is heated at 100 to 200.degree. C., preferably 130 to 150.degree. C., for 0.5 to 6 hours. In the dry method, the water content is 10%, preferably 5%, or less. In the wet method, the water content is 5 to 50%, preferably 20-30. The pH is 3.5 to 8, preferably pH 4.0 to 5.0.
The processed food industry has sought to satisfy consumer demands for foods containing starches which have not been chemically modified but which have the same functional properties as chemically modified starches.
Starches are chemically modified with difunctional reagents, such as phosphorus oxychloride, sodium trimetaphosphate, adipic anhydride, acetic anhydride and epichlorohydrin, to produce chemically crosslinked starches having excellent tolerance to processing variables such as heat, shear, and pH extremes. Such chemically crosslinked starches provide a desirable smooth texture and possess viscosity stability throughout the processing operation and normal shelf life of the food.
In contrast, unmodified (i.e., non-crosslinked) starches breakdown in viscosity, loose thickening capacity and textural qualities, and behave unpredictably during storage as a result of the stresses encountered during food processing. Heat, shear, and/or an extreme pH, especially an acidic pH, tend to fully disrupt the starch granules and disperse the starch into the food. Hence, unmodified starches are generally unsuitable for use in processed foods.